A solid laser, semiconductor laser and gas laser having a large output and a small size, which radiate an ultraviolet ray, visible light or infrared ray having a wavelength of from 300 to 1,200 nm, have become easily available, and these lasers are very advantageous for a recording light source used in the direct plate-making based on digital signal, for example, from a computer.
Various investigations on recording materials sensitive to such laser beams have been made. Representative examples of the recording material include first recording materials capable of being recorded with an infrared laser having a wavelength of not less than 760 nm, for example, positive working recording materials as described in U.S. Pat. No. 4,708,925 and negative working recording materials of acid catalyst crosslinking type described in JP-A-8-276558 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), and second recording materials responsive to an ultraviolet ray or visible light laser having a wavelength of from 300 to 700 nm, for example, negative working recording materials of radical polymerization type as described in U.S. Pat. No. 2,850,445 and JP-B-44-20189 (the term “JP-B” as used herein means an “examined Japanese patent publication”).
On the other hand, recording materials responsive to light having a short wavelength of not more than 300 nm are especially important for photoresist materials. In recent years, the degree of integration is more and more increased in integrated circuits, and the fabrication of super-fine patterns composed of lines having a width of finer than a half micron has been required in the production of semiconductor substrate, for example, VLSI. In order to fulfill such requirements, the wavelength of light source for an exposure apparatus used in photolithography is more and more shortened and the use of a far ultraviolet ray or an excimer laser (e.g., XeCl, KrF or ArF) has been investigated. Further, the formation of super-fine patterns by an electron beam has been started to investigate. Particularly, the electron beam is regarded as a promising light source for the next generation pattern formation techniques.
A problem common to all of these image recording materials is that how much an ON-OFF of the image can be enlarged in the exposed area with various kinds of energy and unexposed area. In other words, how a balance between high sensitivity and good preservation stability of the image recording material can be achieved.
In order to resolve the problem, it is known to use various high sensitive photo-radical polymerizable compositions. In particular, photo-radical polymerizable compositions comprising a radical polymerizable crosslinking agent and a polymer binder are applied to printing plates such as lithographic printing plates and letterpress printing plates.
As the radical polymerizable crosslinking agent, a polyfunctional crosslinking agent having at least two polymerizable groups in its molecule is ordinarily employed in order to enhance crosslinking efficiency. Although an image recording material containing such a polyfunctional crosslinking agent exhibits high sensitivity, the crosslinking agent tends to crystallize in case of using the solid compound or a phenomenon, for example, surface tackiness of the recording material occurs in case of using the liquid compound because of oozing thereof onto the surface, when the recording material is allowed to stand under high temperature and high humidity conditions. Therefore, techniques to further improve preservation stability of the recording material have been desired.
With respect to a printing plate, durability (printing durability) of the printing plate at printing is an extremely important factor. The printing durability is widely varied depending on a photosensitive layer, specifically, the kind of a photo-radical polymerizable composition used, and is largely dominated by the degree of crosslinking after exposure and the hardness of crosslinked film obtained. As a result of recent investigations, it is reported that a factor of the decrease in hardness of crosslinked film due to penetration of developer into the crosslinked film is also important.